Following Paper ID and Roll No. to be filled in your Answer Book

Printed Pages-4 EME6O2

B.Tech.

(sEM. VD THEORY EXAMTNATTON 2011_12

MACHINE DESIGN-II

Time : 3 Hours Total Marks : 100

Notes :-(i) Attempt all questions.

(ii) Assume any missing data suitably.

(iii) Use of design data book is permitted.

1. Attempt any two parts of the following :- (10x2:20)

(a) Describe the law of gearing. Why involute teeth arepreferred over cycloidal teeth ? What is the reason ofinterference in gears and how it can be avoided ?

(b) A pair of spur gear with 20o full depth involute teethhas pinion with 24 teeth and gear with 72 teeth. Thepinion speed is 3000 rpm and it transmits 35 kW. Thepermissible static bending stress for the material ofboth the gears is 140 Mpa. Design the gear.

(c) Two parallel shafts with center distance 200 mm are tr:be connected by 20, full depth spur gear and pinionfor a speed ratio of 3 : l. The speed of the pinion is600 rpm. Module and width of the gear and pinion are5 mm and 50 mm respectively. The safe static stresses

for pinion and gear are 110 and 55 Mpa respectivell,.Find maximum power that can be transmitted safely.

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2. Attempt any two parts of the following :- (10x2=2'A)

(a) Two precision cut forged steel helical gears have 20o

full depth involute teeth. The helix angle is 23o and

permissible static.bending stress is 100 MPa. If gear

ratio is 3 : 1, module is 3 mm, face width is 300 mm

and surface endurance strength is 630 MPa; find the

power transmitted and wear load and state whether the

design is safe. The speed of pinion is 600 rpm.

(b) Design a woffn and worm gear drive for a speed

reduction by 25. Worm rotates at 600 rpm and transmits

35 kW. Assume double start thread and gear has 50

full depth 20o involute teeth.

(c) Using a suitable schematic diagram explain the forces

acting on wonn gears. Also, define normal pitch, helix

angle and efficiency of worm gear drive.

3. Answer any two parts of the following :- (10x2=20)

(a) A deep groove ball bearing has dynamic capacity of

20000 N and is to operate on the following work cycle;

Radial load of 6000 N at 200 rpm for 25Yo time, radial

load of 9000 N at 500 rpm for 20% of the time and

radial load of 3500 N at 400 rpm for the remaining

period. Assuming the loads are steady and the inner

race rotates, find the average expected life ofthe bearing

in hours.

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(b) Select a suitable bearing for a 40 mm shaft that has to

operate 8 hours per day,5 days per week for 5 years

and is to carry d stationary radial load 2500 N at

1500 rpm. The use involve minor shock and inner ring

is rotating.

(c) What are the main components of the rolling contact

bearing. Describe basic static load capacity, basic

dynamic load capacity and life of bearing.

4. Attempt any two parts of the following :- (10x2=20)

(a) Differentiate between hydrodynamic lubrication,

wedge film lubrication and squeeze film lubrication.

What are the advantages and limitations of journal

bearing ?

(b) A full journal bearing of, diameter 80 mm and length

120 mm is to support a load of 20 kN at the shaft

speed of 1500 rpm. The bearing temperature is to be

limited to 75o and the ambient room temperature is

38'. The viscosity of oil used is 0.0088 kg/m-s at 115o.

Check if artificial cooling is required and frnd the

amount of artificial heating.

(c) Desigu a journal bearing to support a load of 5 kN at

1000 rpm using a hardened steel journal and bronze

backed babbit,bearing. The bearing is lubricated by

oil rings. Assume room temperature as 25o and the oil

temperature as 77".

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5. Attempt any one part of the following :- (20x1:20)

(a) The cylinder of a slow speed steam engine is 250 mm

diameter and the steam pressure I N/rnm2. The piston

rod length is 1000 mm and the connecting rod is

1.2 m long. The engine stroke is 550 mm. Determine

the dimensions of the cross section of the connecting

rod assuming the depth to be twice as thickness and a

suitable diameter for the piston rod.

(b) A four stroke diesel engine has the followingspecifications :

Brake power

Speed

Indicated MEP

Mechanical efficiency : 8Ao/o

Determine :

(0 bore and length of the cylinder,

(iD thickness of the cylinder head, and

(iii) size of stud for the cylinder head.

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12 kW

1500 rpm

0.35 N/mmz